The objective of the proposed research is to define interactions between mammalian reovirus RNA and cellular proteins that regulate translation of viral genes. Reoviruses are members of the Reoviridae, which includes non-enveloped viruses of eukaryotes containing segmented, double-stranded (ds) RNA genomes. Reovirus mRNAs are capped but lack a 3' poly(A) tail, present on most cellular transcripts. Despite the absence of a poly(A) tract, reovirus mRNAs are efficiently translated, and protein synthesis during reovirus infection is almost exclusively viral in origin. How reoviruses are able to accomplish such extraordinary dominance over the cellular translation machinery is not understood. Therefore, translation of reovirus mRNAs is a particularly interesting model for studies of translational control mechanisms and identification of novel cellular RNA-binding proteins that regulate protein expression. The central hypothesis of this work is that termini of reovirus RNAs play important roles in translational control of viral gene expression and that the mechanism of regulation involves specific interactions between viral nucleotide sequences and cellular RNA-binding proteins. In Specific Aim 1, cellular proteins that bind terminal nucleotide sequences of reovirus RNA will be identified. In Specific Aim 2, primary nucleotide sequences and higher-order structures in reovirus RNA important for specific protein binding will be defined. In Specific Aim 3, the role of terminal nucleotide sequences in translational regulation of reovirus RNA will be elucidated using gain-of-function and loss-of-function approaches. This research will enhance an understanding of key intermolecular interactions that regulate translation of reovirus RNA, lead to the identification of previously unknown cellular RNAinteracting proteins, and contribute new insights into general principles of RNA-protein interactions. This work will be conducted in the context of a scientific environment and training program designed to establish Dr. Chappell as an independent investigator focused on translational regulation by viruses and cells.